1. Technical Field
The present invention relates to a reel on which a recording tape such as a magnetic tape, generally used as data recording/playback media of a computer, is wound.
2. Related Art
A recording tape cartridge in which a recording tape such as a magnetic tape, which is used as data recording/playback media (data backup) of a computer or the like, is wound on a synthetic resin reel and a single reel is accommodated in a case has been conventionally known. The reel used in this recording tape cartridge includes a hub, and one of upper or lower flanges is integrally formed with the hub and the other of the upper or lower flanges is welded to the hub.
In addition, a reel gear with which a drive gear provided on a drive device side is engageable is annularly formed on an outer surface of a base portion of the reel, and a reel plate to which a magnet provided on the drive device side may be stuck is integrally and coaxially attached by an insert molding on a radially inner side of the reel gear. Also, it is desirable that an outer peripheral surface of a hub of the reel is made a perfect circle in plan view in view of stabilizing a running speed of the recording tape.
However, there are cases in which the outer peripheral surface of a hub 132 is actually formed into a substantial equilateral triangle in plan view, as shown in FIG. 10. In this case, as shown in FIG. 9, three gate regions (gate traces G) without teeth are formed at regular intervals on a reel gear 142 in a reel 130. In a mold, a reel plate 154 is usually held except for at the gate regions (it is not held at the gates), so that three groove portions 196 are formed between the reel plate 154 and portions excluding the gate regions, and the groove portions 196 are not formed between the gate regions and the reel plate 154 (instead, three engagement portions 198 are formed thereat).
Therefore, when a resin material contracts (cools) upon removal from a mold, since the groove portions 196 are not formed at the non-toothed areas of the reel gear 142, that is to say, not formed at the areas at which gate traces G are formed (the engagement portions 198 are formed instead), contraction of the reel plate 154 is suppressed. In addition, since resin pressure is high in the vicinity of the gates (gate traces G), the amount of contraction thereat is lower than that of other portions. Therefore, as shown in FIG. 10, the outer peripheral surface of the hub 132 is formed into a substantial equilateral triangle, having the areas without teeth as apexes thereof in plan view. When the outer peripheral surface of the hub 132 is formed into a substantial equilateral triangle in plan view such as this, the running speed of the recording tape is uneven, causing concerns about reading errors at the drive device side.